A well-known way of capturing and converting solar radiation into a more useful form of energy such as electricity is to use a radiation focusing device (typically in the form of one or more mirrors) to concentrate and focus incident solar radiation on a radiation absorption element (typically a vessel containing a working fluid or an array of photovoltaic cells). As the angle of incidence of the solar radiation changes throughout the course of a day, the relative positions of the radiation focusing device and the absorption element are adjusted to keep the concentrated solar radiation focused on the radiation absorption element. Intuitively, the most practical and cost-effective mechanizations pair a fixed radiation focusing device with an absorption element that moves with respect to the radiation reflector. Representative examples of this approach are disclosed, for example, in the U.S. Pat. Nos. 3,868,823 and 4,071,017 to Russell, Jr. et al., the U.S. Pat. No. 3,994,435 to Barr, the U.S. Pat. No. 4,318,394 to Alexander, and the U.S. Patent Publication No. 2011/0168160 to Martinez Moll et al.
The radiation focusing device may comprise a series of flat mirrors, as disclosed by Russell Jr. et al., but more commonly comprises one or more curved (parabolic, spherical or cylindrical) mirrors, as disclosed by Barr, Alexander, and Martinez Moll et al. As disclosed in each of the foregoing references, the mirrors can be configured as a linearly extending trough so that the reflected solar radiation is focused above the mirrors on a linearly extending line or region that moves in a circular/cylindrical path as the angle of incidence of the solar radiation changes. Such a configuration is particularly advantageous in terms of mechanical simplicity because the radiation absorption element can simply be pivoted about a fixed point aligned with the center of the circular/cylindrical path of focus. But in practice, the disclosed reflector configurations allow significant divergence of the reflected solar energy as the solar angle of incidence strays from an optimal angle. As a result, the energy focused on the radiation absorption element is less concentrated, resulting in less efficient energy conversion. Accordingly, many such systems include a provision for adjusting the curvature of the radiation focusing device as a function of the solar angle of incidence to improve the concentration of solar energy focused on the radiation absorption element. See the aforementioned patent to Alexander, for example. And in mechanizations including a movable radiation reflector, see for example, the U.S. Pat. No. 4,056,309 to Harbison et al. and the U.S. Patent Publication No. 2012/0285440 to Kosaka et al.